PROJECT SUMMARY/ABSTRACT This K99/R00 proposal examines the joint impacts of local alcohol and cannabis policies on violence in California before and after recreational cannabis legalization in 2018. Self-directed and interpersonal violence are leading causes of death and injury in the United States. Changes in alcohol and cannabis use, driven by state cannabis legalization policies, may be important but unrecognized contributors to these outcomes. Alcohol?s role in violence is well established. Evidence on cannabis? effects on violence is limited and mixed. Cannabis legalization could lower rates of alcohol-related violence through cannabis-alcohol substitution. Existing research on cannabis legalization often focuses on state-level variation. However, most states defer to city and county governments to implement cannabis legalization policies, including determining where outlets are located. Local control results in enormous local-level heterogeneity in local policies and outlet density. High geographic density of alcohol outlets increases rates of violence; recent studies report similar patterns for cannabis outlets. In legalizing states, cannabis outlets are being disproportionately co-located with alcohol outlets in low-socioeconomic status (SES) communities. However, no studies examine if and how local alcohol and cannabis policies together contribute to intoxicant saturation (i.e., high densities of both alcohol and cannabis outlets) in low-SES communities. Further, there is no evidence on whether co-located cannabis and alcohol outlets interact to affect the health of community residents. We will perform quasi-experimental geospatial analyses of publicly-derived policy, outlet, and administrative health data to: (1) assess how alcohol and cannabis policies in 241 California cities and counties impact outlet density and geographic co-location; (2) determine the interactive effects of alcohol and cannabis outlet densities on rates of emergency department visits, inpatient hospitalizations, and deaths due to self-harm and assault throughout California; (3) evaluate how the relationships documented above contribute to disparities in alcohol and cannabis outlet co-location, densities, and effects on self-harm and assault. The research plan is complemented by an exceptional mentorship team and training plan at the University of California, San Francisco and NIAAA-funded Prevention Research Center. The plan builds on the applicant?s background in violence prevention research and includes new training in alcohol and drug use as contributors to violence, alcohol and drug control policies, and geospatial statistical methods. The combined research and training plans will prepare the applicant for a successful independent epidemiology research career focused on how to design optimal alcohol and drug policies to prevent violence and reduce health disparities. This research aligns with NIAAA?s strategic goal to evaluate the effectiveness and implementation of new policies for preventing alcohol-related consequences such as violence. This research is urgently needed as other localities consider cannabis legalization and models for regulation.